Sure Flap Connect cat flap?

Hello, can anyone give me advice on the Sure Flap Connect cat flap?

I've had this cat flap for a few months. I've scanned the microchips of four cats, and everything worked fine until yesterday. Since yesterday, I've been getting a notification every few minutes that a new animal (with chip number xy) has been added. This number belongs to one of my cats and has been saved for months.

I unplugged the hub and then plugged it back in. I removed the batteries from the cover and put them back in after a few minutes.

All to no avail. Does anyone know what the problem is?